NutriStack
Calcium and Doxycycline, timing-sensitive.
Calcium chelates doxycycline, forming insoluble tetracycline-calcium complexes that significantly reduce antibiotic absorption. This can reduce doxycycline bioavailability by 20-50%, potentially leading to subtherapeutic levels and treatment failure.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
From the interaction database
What the row says.
Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.
At a glance
- Substances
- Calcium and Doxycycline
- Pair type
- Timing Sensitive
- Evidence (highest tier)
- Strong
- Source citations
- 3 sources
- Stack Score effect
- −5 to your Stack Score (per scored timing-sensitive row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Timing Sensitive · Strong evidence
Timing Sensitive
What is happening. Calcium chelates doxycycline, forming insoluble tetracycline-calcium complexes that significantly reduce antibiotic absorption. This can reduce doxycycline bioavailability by 20-50%, potentially leading to subtherapeutic levels and treatment failure.
Mechanism. Calcium ions chelate doxycycline's beta-diketone system and adjacent hydroxyl groups, forming insoluble calcium-tetracycline complexes. These complexes are too large and insoluble for intestinal absorption and are excreted in feces.
Recommendation. Separate doxycycline and calcium supplements by at least 2 hours. Avoid dairy products (high calcium) within 2 hours of doxycycline dosing. Take doxycycline with water between meals for optimal absorption.
Minimum separation. 120
Sources (3)
- Leyden JJ. Absorption of minocycline hydrochloride and tetracycline hydrochloride: effect of food, milk, and iron. J Am Acad Dermatol. 1985;12(2 Pt 1):308-312. PMID 3973128
- Liu C, Kuang X, Li K, Guo X, Deng Q, Li D. Effects of combined calcium and vitamin D supplementation on osteoporosis in postmenopausal women: a systematic review and meta-analysis of randomized controlled trials. Food & Function. 2020. PMID 33237064
- Yao P, Bennett D, Mafham M et al.. Vitamin D and Calcium for the Prevention of Fracture: A Systematic Review and Meta-analysis. JAMA Network Open. 2019. PMID 31860103
Stack Score
How this pair moves the number.
Effect on the composite score
If both Calcium and Doxycycline are in the same stack, this pair applies −5 to your Stack Score (per scored timing-sensitive row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
Check your full routine
One pair was the worked example. NutriStack runs every pair in your stack at once.
Drop in your supplements and prescriptions and the public database surfaces every interaction, synergy, timing rule, and contraindication, every one linked to its primary source.